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Ultraviolet Light Process Model Evaluation

Ultraviolet Light Process Model Evaluation. Presented by: Jennifer Hartfelder, P.E. Brown and Caldwell. Models to Evaluate UV Performance. USEPA Mathematical Protocol – USEPA Design Manual Municipal Wastewater Disinfection

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Ultraviolet Light Process Model Evaluation

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  1. Ultraviolet Light Process Model Evaluation Presented by: Jennifer Hartfelder, P.E. Brown and Caldwell

  2. Models to Evaluate UV Performance • USEPA Mathematical Protocol – USEPA Design Manual Municipal Wastewater Disinfection • UVDIS – Software Developed by HydroQual, Inc. based on the USEPA Mathematical Protocol • NWRI/AWWARF Protocol – Ultraviolet Disinfection Guidelines for Drinking Water and Water Reuse

  3. UV Process Design Model • Chick’s Law: N = Noe-kIt • N = bacterial concentration remaining after exposure to UV • No = initial bacterial concentration • k = rate constant • I = intensity of UV • t = time of exposure

  4. USEPA - Step 1Calculate Reactor UV Density

  5. USEPA - Step 2Calculate Intensity • Biological Assay • Direct Calculation Method

  6. Intensity FieldPoint Source Summation Method

  7. Intensity vs. UV Density

  8. Lamp Configuration

  9. Average Intensity • Iavg = (nominal Iavg)(Fp)(Ft) • Fp = the ratio of the actual output of the lamps to the nominal output of the lamps • Ft = the ratio of the actual transmittance of the quartz sleeve or Teflon tubes to the nominal transmittance of the enclosure

  10. USEPA - Step 3Determine Inactivation Rates • K = aIavgb

  11. USEPA - Step 4Determine Dispersion Coefficient • Establish relationship between x and u • hL = cf(x)(u)2 • Plot log(u) and log(x) versus log(ux) • Dispersion number, d • d = E/(ux) • d = 0.03 to 0.05 • E = 50 to 200 cm2/sec

  12. USEPA - Step 5Determine UV Loading • Plot log(N’/No) vs. Q/Wn and u vs. Q/Wn

  13. USEPA - Step 6Establish Performance Goals • Np = cSSm • N’ = N - Np

  14. USEPA - Step 7Calculate Reactor Sizing • Number of lamps required: • Q/Wn – determined from the log (N’/No) vs. maximum loading graphs developed in Step 5 for the N’ developed in Step 6 • Lamps required = Q/(Q/Wn)/Wn

  15. Arc length Centerline spacing Watts output Quartz Sleeve Diameter No. of banks in series Aging Factor Fouling Factor Flow Dispersion Coefficient Average Intensity Number of lamps Staggered Percent transmissivity UVDIS Input

  16. UVDIS Output

  17. NWRI/AWWARF Protocol • Determine UV inactivation of selected microorganisms under controlled batch conditions by conducting a bioassay • Dose-Response Curves • Microorganism • MS-2 bacteriophage • E. coli • Pilot vs. full scale study

  18. Bioassay Results

  19. UV Dose • German drinking water standard: 40 mW-sec/cm2 • US wastewater industry standard: 30 mW-sec/cm2 • CDPHE WWTP design criteria: 30 mW-sec/cm2 • US reuse standard: 50 - 100 mW-sec/cm2 • NWRI/AWWARF based on upstream filtration: • Media - 100 mW-sec/cm2 • Membrane - 80 mW-sec/cm2 • Reverse Osmosis - 40 mW-sec/cm2

  20. Protocol Evaluation • For peak hour conditions: • Q = 3.5 MGD (9,200 lpm) • SS = 45 mg/L • No = 1.50E+06 No./100 mL • N = 6,000 No./100 mL • Transmittance = 60% • Allowable headloss = 1.5 inches

  21. System Specific Design Criteria

  22. Number of Bulbs Required Utilizing Various Sizing Methods

  23. Pros Apply same calculations to all systems Can be used for uniform, staggered, concentric, and tubular lamp arrays Cons Least conservative Assumes flow perpendicular to lamp USEPA Mathematical Protocol

  24. Pros HydroQual is in the process of updating the program to address some of the cons More conservative than USEPA protocol Cons Less conservative than bioassay For low-pressure systems only For flow parallel to lamps only Dispersion coefficient, E, is assumed UVDIS

  25. Pros Most conservative May assume a conservative required dose (50 to 100 mW-sec/cm2) Cons Bioassay tests have not been conducted yet for all systems Bioassay is costly Scale-up issues Bioassays have not used the same protocol (i.e., microorganism) More research on how to select required dose is necessary NWRI/AWWARF Protocol

  26. Conclusions • Bioassay is most conservative sizing method • More research required: • Dose selection protective of human health • Scale-up issues • Target organism • Engineer should require a field performance test and performance bond

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